In vacuum holding systems, a vacuum source is connected to a plurality of vacuum cups which are configured to engage a workpiece or other object, or a plurality of workpieces or other objects. When the vacuum source is in operation, the difference in pressure between the vacuum source and each of the vacuum cups results in a tendency for air to be drawn into each of the vacuum cups. If a given vacuum cup is engaged with a workpiece or object, a suction force is created between the object and the cup. Typically, the suction force of a plurality of such cups is utilized to lift and hold a particular object or plurality of objects. Such systems are commonly utilized, for example, in vacuum pick up and place systems used in pallet loading and unloading, where various layers of product, such as soft drinks packaged in various quantities, are placed on and removed from pallets.
In such vacuum holding or pick up and place systems, one problem commonly encountered is that of excessive leakage flow. For example, if one or more of the vacuum cups does not engage the product in a sealed fashion, some amount of leakage flow through the vacuum cup to the vacuum source will occur. Because the typical vacuum source is only capable of creating a certain maximum air flow in the overall system, any such leakage flow reduces the effective suction force of the vacuum cups which engage the product. Thus, the effective holding capacity of the plurality of vacuum cups is diminished. In some cases, where the leakage flow is too great, the vacuum holding system may be rendered ineffective.
In the past, various devices to limit flow losses in vacuum cup holding, or pick and place, systems have been utilized with varying success. For example, orifices to limit flow at each cup to a known value have been utilized. The problem with this approach is that an orifice will pass an increasingly higher flow rate as the pressure differential across it is increased, so, as the system vacuum level increases, the orifice leakage also increases.
In the past, a leaky check valve has also been utilized which would close immediately whenever flow occurred but would still leak enough that it could reopen when the vacuum cup was pressed into sealing contact with a work piece or product. Such leaky check valves presented the same problems as the aforementioned flow limiting orifice, although this approach did initially limit flow losses when vacuum was first applied to the system. However, other problems arose. For example, when using larger vacuum cups, reopening the check valve via leakage flow took too long when picking up a part or product and caused lower productivity due to increased cycle times. Further, the small leakage flow of such fixed-value check valves was also sometimes insufficient to make up for porosity flow passing through a porous work surface and the part or product could not be picked up because the check valve would remain closed. If the check valve leakage rate was increased in response to such problems, such configurations lead back to the excess leakage flow problems associated with larger orifices because inactive vacuum cups leaked continuously through the "closed" leaky check valves, which made larger vacuum pumps necessary, increasing the cost of such systems.
Other devices such as mechanically operated valves have been incorporated into vacuum cup fittings. Such normally closed valves are opened only when a valve stem associated therewith is pressed into contact with a work surface or product surface. Problems with this approach include that work surfaces can be marred by the valve stems and high forces are required to press numerous valves into contact with the work surface or product surface. Further, due to damaged work surfaces, cracks between products, or vacuum cups overhanging the work piece or product edge, some vacuum cups do not effectively seal even when the mechanical valve is actuated, again resulting in undesired leakage flow.
Accordingly, it is desirable and advantageous to provide a flow sensor valve which could be utilized in such vacuum holding systems for preventing excessive leakage flow if, for any reason, substantially sealing contact is not made between the vacuum cup and the work piece or product which is to be handled. It also is desirable and advantageous to provide a flow sensor valve which is adjustable to provide shut-off at predetermined flow rates.
An object of the present invention is to provide a valve construction for a main air flow passage where air flow through such main passage which exceeds a predetermined rate results in shut off of the main passage with negligible leakage flow.
Another object of the present invention is to provide a valve construction for a main air flow passage which valve can be adjusted or tuned such that the shut off point thereof is selectable for various desired applications.
Yet another object of the present invention is to provide a flow sensor valve having a main passage with a shut off valve therein, and a controllable release valve which enables the main passage to be shut off even when the vacuum cup associated therewith is in sealing contact with a work piece or product.
A further object of the present invention is to provide a flow sensor valve having a main passage with a shut off valve therein, and a controllable reset valve which enables the shut off valve of the main passage to be opened without requiring the vacuum source associated therewith to be turned off.
Another object of the present invention is to provide an air pulse distribution system for controlling the operation of release valves and/or reset valves associated with a plurality of flow sensor valves in a vacuum pick and place device.